Update on face-ventilation research for improved longwall-dust control

Longwall mining equipment and operational practices have improved dramatically from the early 1980s through the mid-1990s. Longwall mining now accounts for approximately 50% of the coal produced underground in the United States. Average shift production has increased from approximately 1.36 kt/shift (1,500 st/shift) in 1983 to more than 2.9 kt/shift (3,200 st/shift) in 1994. Historically, longwall mining operations have had difficulty in maintaining compliance with mandatory federal dust standards. In the early 1980s, 31% of the compliance samples collected by the US Mine Safety and Health Administration (MSHA) exceeded the 2 mg/m3 respirable dust standard. For fiscal year 1994, 20% of MSHA-collected samples exceeded the standard. Although significant gains in longwall dust control have been made, these have been overshadowed by the significant increases in coal extraction rates. The increase in coal extraction rates has been accompanied by a continuing effort to maintain compliance with the respirable dust standard. However, as more coal is mined, more dust is generated (Webster, 1990). The increase in long- wall coal-extraction rates has meant that far more dust is being produced, which means that more dust must be controlled. Approximately 25% of longwalls today are capable of extracting in excess of 5.44 kt/shift (6,000 st/shift), with several capable of extraction rates in excess of 9 kt/shift (10,000 st/shift).

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